Instead of political unity, Poland’s Independence Day celebrations a week ago ended up pushing differences to the fore. Tellingly, Warsaw, the capital city, saw not one large-scale parade, but two.

A rally called by President Bronislaw Komorowski attracted more than 10,000 people. With a marching band, a speech on national unity, a cameo by a World War II–era tank and a sprinkling of Polish celebrities, the parade was a feel-good party for one of the few countries in Europe that actually has something — the economy that is — to feel good about. Growth might be slowing, but at 2.4% this year, according to the European Commission, it remains higher than in 22 out of the E.U.’s 27 members.

Within earshot of the presidential parade, however, a large square by the communist-era Palace of Culture began to swell with a sea of Polish flags, nationalist banners and placards. This was the far right’s show, and if its members had anything to celebrate, it was that theirs was the biggest and loudest party in town. For groups that have no representation in parliament, including outfits likes the All-Polish Youth and the National Radicals, the turnout of more than 20,000 was a resounding success. Otherwise, gaiety was in relatively short supply. Crowds shouted antigovernment slogans. Square-shouldered men wearing balaclavas lit red flares. A group of young people tried to torch a 12-starred flag of the E.U. using a lighter, plus what appeared to be a bottle of cologne. (They failed.) “We are at war for Poland,” roared one of the speakers. “We will take Poland back.” From who? Another speaker was specific: leftists and homosexuals. With the governing party being a center-right outfit, the leftists, presumably, were anyone left of the far right.

Janusz Werstler, a teacher, wandered through the crush bearing a Polish flag, a baseball cap and a jacket emblazoned with a red-and-white checkerboard and the numbers 10, 4 and 10. The checkerboard was the insignia of the Polish Air Force. The numbers, meanwhile, represented a date — that of a tragedy that has shaken Polish politics to the core.

On April 10, 2010, an airplane carrying Polish President Lech Kaczynski, his wife and 94 others crashed near Smolensk, in Russia, killing everyone on board. An official inquiry into the crash, concluded last year, blamed poor weather conditions, pilot error and inadequate airport facilities. Werstler, however, along with a group of others who joined the march, believed he knew better. “Everything points to one conclusion,” he said. “It was an assassination.”

The far right may not have paid them sufficient lip service during the march, but supporters of Werstler’s theory can rely on more powerful political allies. Citing its own investigation, as well as flaws in the government’s, the main opposition party, Law and Justice (PiS), has openly claimed that the crash was deliberately planned. PiS’ case appeared to gain support at the end of October, when one of the country’s biggest newspapers reported that traces of explosives had been found aboard the wrecked plane. Within hours, Jaroslaw Kaczynski, the party’s leader and the deceased President’s twin brother, proclaimed that the crash victims had been “murdered” and called on the government of Prime Minister Donald Tusk to resign. A day later, however, acknowledging that it did not have incontrovertible evidence (“Those could have been explosives, but not necessarily,” a statement read), the paper in question retracted the story. Its author and the editor in chief were sent packing. Kaczynski, expected to backtrack, did not. There was “a 99% chance,” he said, that the crash had been “an assassination.”

To the governing coalition headed by Tusk’s center-right Civic Platform (PO), and to much of the commentariat, Kaczynski’s accusations were just as inflammatory — pandering to right-wing radicals, Russophobes and the conspiracy-minded — as they were groundless. Recently, they earned PiS a tongue lashing by Zbigniew Brzezinski, a onetime national-security adviser to Jimmy Carter and an anticommunist icon in Poland. “There are people who, consciously or subconsciously, maybe because they’re sick, divide society and undermine the credibility of the state, of the government and of justice,” Brzezinski said. “Let them say clearly who they think the murderers are.” Although Kaczynski is yet to oblige, some of his supporters have no qualms about blaming Russia and accusing Tusk’s government of helping it in the “cover-up” that ensued.

Tusk, of course, hasn’t done himself any favors. In the face of Russian negligence in documenting the cause of the crash, his government has often appeared passive and weak. It has also been taken to task after exhumations revealed that several of the crash victims’ bodies — including those of Poland’s last communist-era President in exile and a Solidarity hero — had been misidentified, and buried in the wrong graves as a result.

All of this has clearly not helped put the controversy to rest. According to recent polls, as many as 1 in 3 people is now convinced that the crash was in fact an assassination. Perhaps even more worrying for Tusk is how little confidence Poles place in his government’s ability to dispel the remaining doubts: 63% demand that the task fall to an international commission.

Boosted by the public backlash over the burial mix-ups, a banking scandal involving the Prime Minister’s son, new austerity measures and signs of an economic slowdown, PiS had climbed to a lead in the polls last month, the first time in years. With his most recent outbursts, however, Kaczynski seems to have squandered the recent gains. A poll released last week showed that PiS had fallen 12 points behind Tusk’s PO. “For the past few moths, PiS wisely left Tusk to deal with his own problems,” Michal Kaminski, a former Kaczynski ally, told the daily Gazeta Wyborcza. “That strategy now lies in ruins.”

Even the man proposed by PiS as the head of an interim “technocrat” government — in the unlikely event that Tusk loses a vote of confidence — grumbled that Kaczynski had yet again planted the crash smack in the center of Polish politics. He understood the “emotional reaction,” the mild-mannered Piotr Glinski said, but regretted “that it changed both the atmosphere and the priorities on the political scene.”

With PiS in danger of losing the political center once and for all, Kaczynski can ill afford to get into bed with the far right. This is possibly why he stayed away from the nationalists’ Independence Day rally on Nov. 11, preferring to visit his brother’s tomb instead.

Political instinct seems to have served him right. Only 15 minutes into the march, hundreds of protesters, many of them in balaclavas, began to clash with riot police. The melee soon spilled into one of the side streets. Fragments of pavement traveled in one direction, tear gas flowed in the other. Some of the rioters threw flares at the windows of a local LGBT association.

No more than 20 ft. away from a row of five or six cops who fired rubber bullets into the air, stood Maria, a 68-year-old PiS supporter. She had come out to protest, she said, because “the country had been sold out to the E.U., to special interests.” And “of course, because of Smolensk.” She didn’t condone the rock throwing, however. She was outraged, yes, but only to a point.